Ignitron



June 5, 1956 w. w. RIGROD 2,749,483

IGNITRON Filed Aug. 29, 1951 INVENTOR W 14 E/C FFQP United States Patent IGNITRON William W. Rigrod, Bloomfield, N. J., assignor to Westmghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 29, 1951, Serial No. 244,231

4 Claims. (Cl. 315-261) This invention relates to Ignitrons and, more particularly, to ignitrons having a mercury pool or other reconstructable liquid cathode.

An object of the invention is to increase the probability of ignitor are forming each time it is required.

A further object of the invention is to reduce the current and voltage passing through the ignitor to form an arc. i

A further object of the invention is to reduce the sur face tension of the pool cathode for promoting ignitron process.

Another object of the invention is to ruffie the surface of the pool cathode or produce irregularities thereon for obtaining field-emission peaks.

Specifically, the invention contemplates use of heat and cathode agitation as means for accomplishing the beneficial purposes of the invention.

Other objects of the invention will appear to persons skilled in the art to which it appertains as the description proceeds, both by direct reference thereto and by implication from the context.

The single figure of the accompanying drawing is a vertical section of an ignitron wherein my invention is incorporated.

In the specific embodiment of the invention illustrated in said drawing, the ignitron shown therein comprises an inner cylindrical wall surrounded by a water jacket 11 and having a pool cathode 12 of mercury or other reconstructable fluid resting on a header 13 closing the bot-tom portion of the device. It will be understood that the upper end of cylinder 10 is also closed and the device evacuated so as to promote exclusive presence of mercury vapor. An anode 14 is located in the upper portion of the device and is, of course, insulated therefrom as usual. A high resistance ignitor 15 has its conical tip partially immersed in the cathode pool '12 and is supported at its upper end by a transverse arm 16 the other end of which is welded to a connection 17 leading to the exterior of the device through an appropriate seal 18. A horizontal baffle 19 is provided above the middle part of the cathode pool and above the ignitor 15.

The basis of the present invention resides in the discovery that an ignitor will strike an arc with greater assurance, or less ignition energy, by creating a disturbance in the normal static condition of the cathode pool favorably aftecting the surface characteristic thereof to promote electric field strength between the ignitor and the pool cathode. According to my invention, this desideraturn is accomplished by raising the temperature of the mercury in the vicinity of the .ignitor and by agitation of the mercury, particularly at the upper surface thereof. It appears, according to my investigations, that the probability of an ignitor striking an arc in a mercury pool rectifier is greater with increase of the temperature of the mercury in the immediate vicinity of the ignit-or-rnercury junction approximately in proportion to the cube of the elec tric field strength above a critical minimum operating value. The influence of increased mercury pool temperature on the ignition process seems to be exerted in two ways, namely (1) it reduces the surface tension, and (2) increases the number and size of minute humps on the mercury surface. These humps are drawn out by the electric field provided by the ignitor until the surface is ruptured. The field strength in the peaks of these humps then attains values sufficiently high for field emission to occur, leading to arc striking. Since presence and growth of these humps on the mercury surface appear desirable, production thereof by thermal means may be augmented by agitation, and according to the present invention, I show this dual application of the beneficial forces operative upon the mercury in the vicinity of the ignitor. While various constructional embodiments of the invention might be shown, the drawing arbitrarily selects and illustrates one only for exemplary purposes.

It may be opportune to observe here that an increased temperature of a mercury pool in general causes increased vapor pres-sure in the igni-tron and consequently increases are drop and likelihood of arc-backs. For this reason, as well as to minimize vapor streaming, my invention contemplates restriction upon the mercury heating, and in :the selected embodiment applies the heat in a restricted part of the pool, admitting of a temperature gradient between the mercury in this region and from the main body of the pool.

T he arbitrarily selected construction comprises a double walled or hollow collar 20 projecting upwardly from the bottom header 13 coaxial with the igni-tor 15 and of less height than the pool depth so that the region within the collar will be kept filled with mercury. Between the walls of this collar is an electric heating coil 21. In practice, this 'coil will preferably be located as close to the inner wall of the hollow collar as presence of adequate insulation will permit and will be somewhat further from the outer wall of the collar with heat insulation therebetween so that the heat from the coil will be transmitted more especially through the inner wall of the collar and heat the mercury pocketed in the collar without seriously affecting the temperature of the mercury at the outside of the collar. In view of the heat being applied :to the mercury within the collar, the mercury will be affected by a local fluid current or circulation which disturbs the surface, and due both to that disturbance and the elevated temperature, enhances the humpy condition of the surface and promotes the arc-striking characteristic thereof.

Greater agitation and positive assurance of a ruffled surface on the pool at the restricted area thereof around the ignitor constitutes a further feature of this invention. For that purpose, the lower rim of the inner wall of the hollow collar is shown sealed to a diaphragm 22 which closes the bot-tom of the collar thereat. A sonic or supersonic vibratory force is applied to this diaphragm and being transmitted through the mercury resting on the diaphragm, obtains a pronounced milling of the overlying mercury surface. As one means for applying a vibratory force, the diaphragm 22 may be made of iron to cooperate as an armature for an electromagnet 23 situated thereunder with its pole piece in proximity to the middle of the diaphragm. A pulsating or oscillating current from any suitable source and at the desired frequency may be connected to the magnet. While the agitation or surface ruffling thus obtained is ample for the purpose desired, yet it is not so violent or of such a great amplitude as to result in the ejection of any droplets of mercury onto the anode.

I claim:

1. An ignitron having a pool cathode and an ignitor, said ignitor being partially immersed in said pool cathode, means restricting a portion of the cathode pool to the vicinity of said ignitor, said restricting means extending from the bottom of said cathode pool substantially to and underlying the top surface of said cathode pool, said restricting means being coaxial to said ignitor, and means coaxial to and effective in said restricted portion of the cathode pool, said means being creative of a modified surface condition of said restricted portion of said pool.

2. An ignitron having a pool cathode and an ignitor, said ignitor being partially immersed in said pool cathode, means restricting a portion of the cathode pool to the vicinity of said ignitor, said restricting means extending from the bottom of said cathode pool substantially to and underlying the top surface of said cathode pool, said restricting means being coaxial to said ignitor, and a heater located entirely below said top surface and coaxial to and effective upon the restricted portion of said cathode pool, said heater being creative of a modified surface condition of said restricted portion of said pool.

3. An ignitron having a pool cathode and an ignitor, said ignitor being partially immersed in said pool cathode, means restricting a portion of the cathode pool to the vicinity of said ignitor, said restricting means extending from the bottom of said cathode pool substantially to and underlying the top surface of said cathode pool, said restricting means being coaxial to said ignitor, and vibratory means located entirely below said top surface and coaxial to and effective upon the restricted portion of said cathode pool, said vibratory means being creative of a modified surface condition of said restricted portion of said pool.

4. An ignitron having a pool cathode and an ignitor, said ignitor being partially immersed in said pool cathode, means restricting a portion of the cathode pool to the vicinity of said ignitor, said restricting means extend ing from the bottom of said cathode pool substantially to and underlying the top surface of said cathode pool, said restricting means being coaxial to said ignitor, a heater and vibratory means, both said heater and said vibratory means being located entirely below said top surface and being coaxial to each other and coaxial to and eifective upon the restricted portion of said cathode pool, both said heater and said vibratory means being creative of a modified surface condition of said restricted portion of said pool.

References Cited in the file of this patent UNITED STATES PATENTS 1,657,495 Breisch Jan. 31, 1928 1,843,495 Pilon Feb. 2, 1932 2,217,436 Evans Oct. 8, 1940 2,379,620 Bowles et al July 3, 1945 2,427,999 Winograd Sept. 23, 1947 2,438,179 Mason Mar. 23, 1948 2,512,299 Boyer June 20, 1950 2,557,774 W-armoltz June 19, 1951 

